Fast equalizer training and frame synchronization algorithms for discrete multi-tone (DMT) system

Abstract

A modem selectively operated in the voice and higher frequency band which supports multiple line codes. The modem uses a digital signal processor so that different existing ADSL line codes can be implemented on the same hardware platform. The modem negotiates in real-time for a desired line transmission rate to accommodate line condition and service-cost requirement. The line code and rate negotiation process may be implemented at the beginning of each communication session through the exchange of tones between the modems. A four-step MDSL modem initialization process is provided for line code and rate compatibility. A synchronization startup procedure for DMT based MDSL modems is provided. The handshake protocol and receiver algorithm allow reliable standard telephone twisted-pair wire. The algorithm makes use of a short length sequence to train a synchronizing equalizer at the receiver. After training to this sequence, a matched filter or correlator is used to detect the inverted sync sequence. The detection of the inverted sequence signals the start of the normal reference training of the DMT equalizers. The MDSL line connection management process provides a simple, efficient, and flexible interface to manage the line connection between MDSL-C and MDSL-R in the telecommunication WAN environment. An internal state machine in an MDSL modem records and monitors the line status and notifies the state change to the other MDSL and also to the host processor. The protocol used for exchanging line connection management messages is a simplified LCP for MDSL.

What is claimed is: 
     
       1. A method for DMT modem initial synchronization, comprising the steps of: (i) a training sequence for probing the length of channel impulse response including repetitive data blocks with the block polarity alternating periodically,   (ii) deriving residual channel inter-symbol interference and frame boundary by subtracting a previously received data block from a current received data block,   (iii) time domain equalizer training by using said training sequence and said residual channel inter-symbol interference to update equalizer coefficients, and   (iv) frame synchronization by using said training sequence and said frame boundary.   
     
     
       2. The method of claim 1 wherein said training sequence is detected, comprising the steps of: comparing the power of the currently received data block to the power of the data block constructed by adding the current received data block to the previously received block.